There are a number of medical treatments, such as ultrafiltration, apheresis and dialysis, that require blood to be temporarily withdrawn from a patient, treated and returned to the body shortly thereafter. While the blood is temporarily outside of the body, it flows through an “extracorporeal blood circuit” of tubes, filters, pumps and/or other medical components. In some treatments, the blood flow is propelled by the patient's blood pressure and gravity, and no artificial pump is required. In other treatments, blood pumps provide additional force to move the blood through the circuit and control the flow rate of blood through the circuit. These pumps may be peristaltic or roller pumps, which are easy to sterilize, are known to cause minimal clotting and damage to the blood cells, and are inexpensive and reliable.
Brushed and brushless DC motors are commonly used to rotate peristaltic pumps. A motor controller regulates the rotational speed of blood pumps. The speed of a pump, expressed as rotations per minute (RPM), regulates the flow rate of the blood through the circuit. Each revolution of the pump moves a known volume of blood through the circuit. The blood flow rate through the circuit can be easily derived from the pump speed. Accordingly, the pump speed provides a relatively accurate indicator for the volume flow of blood through an extracorporeal circuit.
Existing blood pump controllers include various alarms and interlocks that are set by a nurse or a medical technician (collectively referred to as the operator), and are intended to protect the patient. In a typical dialysis apparatus, the blood withdrawal and blood return pressures are measured in real time, so that sudden pressure changes are quickly detected. Sudden pressure changes in the blood circuit are treated as indicating an occlusion or a disconnect in the circuit. The detection of a sudden pressure change causes the controller to stop the pump and cease withdrawal of blood. The nurse or operator sets the alarm limits for the real time pressure measurements well beyond the expected normal operating pressure for the selected blood flow, but within a safe pressure operating range.
Existing controllers do not distinguish between minor blood pump problems that can be safely and easily solved automatically by the controller or by the patient, and more serious problems that require a nurse or other medical professional to attend to the patient and blood circuit. For example, existing controllers typically stop their pumps and issue alarms, upon detection of a partial occlusion in the blood circuit. In response to each alarm of an occlusion in the blood circuit, a nurse attends to the patient, inspects the blood pump and associate catheters, and restarts the pump. Until the nurse restarts the blood pump, the filtration treatment is being delayed.
Partial occlusions in a blood circuit are relatively common occurrences. Nurses frequently have to attend to patients and extracorporeal blood circuits to correct partial occlusions. The delay in restarting the blood pump extends and exacerbates the blood treatment, which may be a period of several hours. The frequent alarms for partial occlusions increase the workload on nurses and the amount of time that they must devote to an individual patient undergoing ultrafiltration treatment.
U.S. Pat. No. 4,227,526 describes a home-treatment dialysis machine that issues audio instructions to the patient on how to correct certain malfunctions, including excessive pressure in the extracorporeal blood circulation circuit. This device is intended for use at home, where there is no nurse or other medical professional present. The dialysis machine disclosed in the '526 Patent does not discriminate between minor dialysis malfunctions that should be treated by the patient, and more serious malfunctions that require treatment by a nurse. U.S. Pat. No. 6,026,684 describes a blood drawing apparatus that detects low blood flow in the blood withdrawal catheter and prompts a patient to restore blood flow by squeezing a hand gripper. The device disclosed in the '684 Patent also does not discriminate between minor occlusion problems and more serious problems. In addition, the devices disclosed in the '526 Patent and in the '684 Patent do not allow a patient to differentiate between withdrawal and infusion lines of a blood circuit. With the devices disclosed in the '526 and '684 Patents, a nurse is not informed as to serious problems, and with minor occlusion difficulties there is no indication as to whether the difficulty has arisen in the withdrawal or infusion catheters, which are generally inserted in different arms of the patient.